Viewing instruments, such as endoscopes, are generally well known in the art. Generally, an endoscope is a medical device for insertion into a body passageway or cavity that enables an operator to view and/or perform certain surgical procedures at a site inside a patient's body. As is known, endoscopes may be either rigid or flexible, and generally include a long tubular member equipped with, for example, some type of system for transmitting images to the user, and in some cases, a working channel for a surgical instrument. The endoscope has a proximal end that remains external to the patient, from which the operator can view the site and/or manipulate a surgical instrument, and a distal end having an endoscope tip for insertion into the body cavity of the patient.
Traditionally, these instruments have used relay optics, such as rod lenses, fiber optic bundles, or relay lenses to transmit the images from inside the body cavity of the patient to the user's eye, located at the proximal end of the endoscope, or to a camera likewise connected to the scope for subsequent display on a monitor and/storage on an image capture device.
These traditional arrangements suffer from a number of disadvantages. First, though systems for designing, constructing, and assembling relay systems have been around for some time, these systems continue to be costly, to be time-consuming, and to demand specialized expertise. Additionally, relay systems typically employ a large number of optical components, which must be precisely fabricated and positioned in order to achieve satisfactory image quality. Finally, image degradation is inevitable with such assemblies due to the fact that the light reflecting from the viewing objects must pass through a series of optical surfaces, as back-reflection, stray light, lens surface roughness, inaccuracies in lens curvatures, and slight lens misalignments all serve to reduce image quality.
Therefore, in order to attempt to circumvent these drawbacks, various designs have been proposed. For example, it has been suggested to use an endoscope with a miniature television tube located in its distal tip, such as the design disclosed in U.S. Pat. No. 2,764,149 to Sheldon. Likewise, other designs with distal imaging devices have been described in U.S. Pat. No. 4,074,306 to Kakinuma et al. and U.S. Pat. No. 4,253,447 to Moore et al. However, while such distal imager designs are effective for flexible and fixed-angle rigid endoscopes, they have, thus far, not worked well for endoscopes with a variable direction of view.
Examples of variable direction of view scopes are disclosed in U.S. Pat. No. 3,856,000 to Chikama et al., U.S. Pat. No. 4,697,577 to Forkner, U.S. Pat. No. 6,371,909 to Hoeg, et al., U.S. Pat. No. 6,500,115 to Krattiger et al., and U.S. Pat. No. 6,560,013 to Ramsbottom. The operating principles of such a scope are illustrated schematically in FIG. 1. A variable direction of view endoscope includes a shaft 10 having a proximal end 12. Such an endoscope has a view vector 14 with an attendant view field 16 having at least two degrees of freedom 18, 20. The first degree of freedom 18 permits rotation of the view vector 14 about the longitudinal axis 22 of the shaft 10, which allows the view vector 14 to scan in a latitudinal direction 24. The second degree of freedom 20 permits rotation of the view vector 14 about an axis 26 perpendicular to the longitudinal axis 22, which allows the view vector 14 to scan in a longitudinal direction 28. A third degree of freedom 30 may also be available because it is usually possible to adjust the rotational orientation of the endoscopic image.
Referring to FIGS. 2A-B, the operating principles of a dual reflector variable direction of view scope are illustrated. A first prism 32 refracts incoming light along a path 34 to a second prism 36, which delivers the light to an optical relay system 38 housed by a hollow transmission shaft 40. The first prism 32 is pivotable about an axis 26 and can be actuated by the transmission shaft 40 through a gear 42 to scan in a plane normal to the page. This optical assembly is covered by a glass dome 43 and supported by a mechanical structure 44, which forms the distal portion of the endoscope.
Such scopes have been unable to employ a traditional optical relay system as efficiently as is possible due to the fact that, as illustrated, these scopes use movable reflecting/refracting elements to change the endoscopic line of sight, and therefore, require complex designs for the distal end of the endoscope such that the tip is capable of folding the optical path and accommodating a miniature transmission mechanism. As a result, less room is available for an optical relay system, the performance of which decreases as its cross-section decreases. Therefore, a variable direction of view endoscope will necessarily have an inferior image quality than a fixed-angle scope of the same diameter when employing a relay lens system.
However, as noted above, thus far, employing a distal imager in the endoscope tip (instead of using a relay system) in order to maintain good image quality has not yet been accomplished as effectively as is possible, as it has proved to be very challenging to do so while, at the same time, keeping the endoscope diameter small. Examples of such systems have been described in Hoeg, as well as, U.S. Pat. No. 5,762,603 to Thompson and U.S. Pat. No. 6,648,817 to Schara et al, which disclose variable direction of view scopes employing pivotable image sensors. However, such pan-tilt schemes are difficult to implement compactly.
A variable direction of view endoscope with a pivotable distal imager is illustrated in FIG. 3A. An electronic image sensor 46 is located at the tip of the scope shaft 10 and pivots about an axis 26. This arrangement requires too much room to be able to fit within standard diameters of a significant number of standard endoscopes because the sensor 46 requires integrated objective optics 48 and flexible cabling 50. Because the solid state imaging device requires a set of lenses between the object being viewed and the image plane of the sensor, this assembly must sweep out a large radius when pivoted, which is simply too large for many endoscopic applications. Additionally, the cabling 50 limits the available scan range. Additionally, the mechanisms required to support and actuate such pivotable sensors require some complexity. An alternative, similar design, illustrated in FIG. 3B, experiences these same disadvantages.
A few designs have been proposed employing a side-mounted, stationary camera in order to minimize the required space, such as those disclosed in U.S. Pat. No. 4,890,159 to Ogiu, U.S. Pat. No. 5,166,787 to Irion, and U.S. Patent Application Nos. 2001/0031912 and 2002/0068853 by Adler. However, while these designs may be space-efficient, none of these devices are able to provide the same viewing versatility that is currently possible by employing a mechanism that enables a variable direction of view.
What is desired, therefore, is a viewing instrument having a variable direction of view that minimizes image degradation. What is further desired is a viewing instrument having a variable direction of view that can be employed in a small diameter. What is also desired is a viewing instrument having a variable direction of view that maximizes the scan range of the instrument.